Particles have many applications in industry, research and medicine, among others. A particle can be ascribed several physical or chemical properties (such as volume or mass). As the size of a particle decreases, these properties change as compared to the bulk metal. The size, and hence the surface area of a particle, can impact the physical, chemical and/or pharmacologic properties of the material forming the particle.
Within this broad arena, particles with a size in the micro or nano scale are useful in a wide variety of applications. Nanoparticles are generally understood to encompass microscopic particles with at least one dimension less than 100 nm, while microparticles are generally understood to encompass particles in the range of 0.1 to 100 μm in size. In a further area, nanoparticles fabricated of magnetic materials have attracted increasing interest among researchers of various fields due to their promising applications in such diverse areas as biomedicine, magnetic resonance imaging (MRI), cell and DNA separation, drug delivery, gene cloning, hyperthermia for cancer therapy, and magnetic recording media.
Naked metallic particles are chemically highly active, and are easily oxidized in air, which can result in loss of magnetism and/or dispersibility. Particles with small size, e.g., less than 10 nm, have more active surfaces and could easily interact with any matrix materials (e.g., H2O and/or chemicals around them during their preparation stage). Therefore, maintaining the stability of metal particles for an extended period without agglomeration or precipitation is an important issue. Stability is a crucial requirement for almost any application of metallic particles. Especially pure metals, such as Fe, Co, Ni, Mn, Ti, Cr, Ca Al, Ag and Zn and their metal alloys, are very sensitive to air. Thus, a significant difficulty for use of pure metals or alloys arises from their instability towards oxidation in air; moreover, the susceptibility towards oxidation becomes higher the smaller the particles are. Particles in the micro- and nano-scale range exhibit intrinsic instability over longer periods of time. Such small particles tend to form agglomerates to reduce the energy associated with the high surface area to volume ratio of the micro- or nano-sized particles.